The present invention relates to a method for rolling steel sections, such as steel piles having flanges or flange-like portions using a train of shaping rolling stands and a universal rolling stand.
In the past, such steel sections were usually produced by a shaping rolling method using rolling stands each fitted with upper and lower horizontal rolls, hereinafter generally called shaping rolling stands. They include breakdown stands, roughing stands, intermediate rolling stands and finishing rolling stands. More recently, however, as disclosed in Japanese Patent Publication No. 47-47784, there is a trend particularly in the rolling of H sections to employ a universal rolling stand fitted with a pair of horizontal rolls and a pair of vertical rolls in conjunction with the shaping rolling stands. This rolling method is herein called "the universal rolling method".
The general differences between the shaping rolling method and the universal rolling method are illustrated schematically in FIG. 1 in connection with the rolling of steel sheet piles. The difference between the shaping rolling method shown in FIG. 1(a) and the universal rolling method shown in FIG. 1(b) lies in the manner in which the intermediate rolling passes (K-6, K-5 and K-4 in FIG. 1(a)) are changed. In the shaping rolling method these are shaping rolling passes whereas in the universal rolling method they are universal rolling passes. All other rolling passes of the universal rolling method are the same as those in the shaping rolling method. Adoption of the universal rolling method makes it possible to start with a steel bloom 2 of rectangular cross section as shown in FIG. 1(b) instead of the conventionally required roughly shaped beam blank 1 shown in FIG. 1(a) and results in simplification of the breakdown rolling process, reduction of roll unit cost and easier adjustment of the contour and dimensions in the rolling of steel sections. These advantages contribute to the development of more economical rolling methods for producing steel sections having very precise contour and dimensions.
The universal rolling method is, however, not completely free from defects and, in particular, involves the following two problems:
(1) Because a bloom of rectangular cross section is used in place of the conventionally used beam blank, the starting material used in the universal rolling method has a greater cross sectional area than that used in the conventional method. Therefore, when the nature of the facilities makes it necessary to maintain a fixed magnitude of product elongation, it becomes necessary to use starting materials having a shorter length. This, in some cases, results in lowering of the rolling yield, the heating furnace productivity, etc. Therefore, in order to eliminate this disadvantage, it is necessary to provide a rolling method which can use a starting material of rectangular cross section which is as long and thin as possible.
(2) It is generally more difficult to obtain a steel section of the desired final contour when a starting material with a rectangular cross section is used than it is when a roughly shaped beam blank is used and a considerable number of shaping rolling passes are nevertheless required before the universal rolling pass.